【作者】 张青；

【导师】 商建东；

【作者基本信息】 郑州大学 ， 测绘科学与技术， 2022， 硕士

【摘要】 在陆地生态系统物质循环和能量流动的过程中,植被承担着举足轻重的作用,同时,随着全球环境变化和全球变暖问题日益严重,地表植被覆盖度也成为区域生态环境健康的重要指标。三江源地区位于青藏高原的腹地,是长江、黄河和澜沧江的发源地,具有重要的水资源存储和生态保护功能,因此,研究三江源地区植被覆盖时空变化特征及其驱动因素,对于保护三江源地区的生态系统稳定性具有重要意义,也能为植被保护提供行之有效的科学依据。本文基于2000～2019年MODIS NDVI数据,综合运用最大值合成法、一元线性回归、空间趋势分析、变异系数等方法,对三江源地区植被覆盖时空演变规律进行了研究,在揭示植被覆盖时空分布特征的基础上,引入地理探测器和地理加权回归模型,对植被覆盖变化影响因素的驱动机理进行了探讨。得出以下主要结论:(1)在年际尺度上,三江源地区NDVI呈现波动上升趋势,变化斜率为0.014/10a。在空间分布格局上,三江源地区20年NDVI均值介于-0.05～0.91之间,整体呈现出“西北较低,东南较高”的分布特征,NDVI>0.5的区域占总面积的49.64%,总体来说,NDVI高值区域主要集中在澜沧江源和黄河源的大部分地区,低值区域集中在长江源西北部。(2)在空间变化趋势方面,三江源大部分区域的NDVI都得到改善,其中,明显改善的面积百分比为22.81%,轻度改善的面积占比为41.85%,以黄河源流域东北部及长江源流域西北部地区改善效果较为明显,明显退化的区域占比较少,零星分布在研究区域的中部,但在动态持续性方面,NDVI未来变化趋势不确定的区域占比在70%以上,持续性明显改善区域仅占总面积的6.19%,多分布在黄河源东北部,需要引起关注和重视。在空间稳定性方面,主要表现为高低波动区域共同存在,低波动区域占比高。(3)由地理探测器的结果可知,气候因素是影响NDVI空间分异的主要因素,且解释力水平存在波动,降水、气温和光照时长在探测中一直处于主导影响地位。不同驱动因子之间的交互作用均大于单因子探测,以双因子增强为主,小部分交互作用类型为非线性协调增强,说明三江源地区植被覆盖空间分异的过程是多种因子之间交互作用的结果。风险探测表明,NDVI与降水呈现明显的正相关作用,而与日照时长、风速则呈明显的负相关作用,温度、相对湿度均在第七分区所对应的NDVI均值最高,适宜植被生长的地貌类型和土壤类型分别为中起伏山地和黑毡土,砂土含量和黏土含量分别为45.4%～49.8%和22.9%～26.9%时,植被长势情况较好。(4)结合地理加权回归模型,对NDVI影响因子回归系数进行空间可视化分析,探索了不同影响因子对三江源地区植被覆盖的影响及其空间异质性。结果表明,植被覆盖变化的影响因素及其影响程度差异较大,降水、气温、黏土含量对植被的影响多呈正向效应,风速、砂土含量对植被覆盖的影响多呈负效应。其中,在研究区东北部以及长江源中北部地区,NDVI受降水、黏土含量影响显著,在降水较为丰富的东南部以及中南部地区,受气温、砂土含量影响显著,而在黄河源西北部,风速对植被覆盖的影响显著。更多还原

【Abstract】 Vegetation plays an important role in the process of material circulation and energy flow in terrestrial ecosystems.At the same time,with the increasingly serious problems of global environmental change and global warming,surface vegetation coverage has become an important indicator of regional ecological environment health.Source area is located in the hinterland of qinghai-tibet plateau,is the birthplace of the Yangtze river,Yellow River and lancang river,have important function of water storage and conservation,as a result,the source area of spatial and temporal variation characteristics of vegetation cover and its driving factors,to protect the ecosystem stability of source area is of great significance,also provide effective scientific basis for vegetation protection.Based on MODIS NDVI data from 2000 to 2019,the integrated use of the maximum synthetic method and monadic linear regression,spatial trend analysis,methods of variation coefficient,the area of three rivers the space-time evolution of vegetation was studied,in time and space distribution of vegetation characteristics on the basis of introducing the geographical detector and geographically weighted regression model,The driving mechanism of influencing factors of vegetation cover change was discussed.The main conclusions are as follows:(1)On the interannual scale,NDVI in the Three-River Headwaters region showed a trend of fluctuation,with a slope of 0.014/10 a.In terms of spatial distribution pattern,the mean VALUE of NDVI in the three-River headwaters region is between-0.04 and0.91 in the past 20 years,showing the overall distribution characteristics of "lower in the northwest and higher in the southeast".The areas with NDVI>0.5 account for 49.64%of the total area.In general,the areas with high NDVI values are mainly concentrated in most areas of the Source of lancang River and Yellow River.The low values are concentrated in the northwest of the source of the Yangtze River.(2)In terms of spatial variation trend,NDVI in most areas of the Three-River Headwaters region has been improved.The area percentage of obvious improvement is 22.81%,and the area proportion of slight improvement is 42.85%.The improvement effect is more obvious in the northeast of the Yellow River headwaters basin and the northwest of the Yangtze River Headwaters Basin,and the area of obvious degradation is less.However,in terms of dynamic persistence,the areas with uncertain future NDVI trends account for more than 70%,and the areas with obvious continuous improvement only account for 6.19%of the total area.Most of them are distributed in the northeast of the Source of the Yellow River,which needs to be paid attention to.In terms of spatial stability,it is mainly manifested by the co-existence of high and low fluctuation regions and the high proportion of low fluctuation regions.(3)It can be seen from the results of geographical detector that climate factors are the main factors affecting the spatial differentiation of NDVI,and the explanatory power level fluctuates.Precipitation,temperature and light duration are always the dominant factors in the detection.The interaction between different driving factors was greater than that of single factor detection,with two-factor enhancement as the main factor,and a small part of interaction type was nonlinear coordination enhancement,indicating that the process of spatial differentiation of vegetation cover in the Threeriver Headwaters region was the result of interaction between multiple factors.Risk detection showed that NDVI and precipitation present obvious positive correlation,while with sunshine duration and wind velocity was significantly negative correlation function of the temperature,relative humidity and evaporation capacity are in the seventh division of the highest average NDVI and vegetation growth well geomorphic types and soil types of ups and downs in the mountain and felt of black soil,respectively,When the sand and clay contents were 45.4%～49.8% and 22.9%～26.9%,the vegetation growth was better.(4)Combined with the geographical weighted regression model,the spatial visualization analysis of the regression coefficients of NDVI impact factors was carried out to explore the effects of different impact factors on vegetation coverage in the Three-River Headwaters region and its spatial heterogeneity.The results showed that there were significant differences in the influencing factors and degree of spatial change of vegetation cover.The effects of precipitation,air temperature and clay content on vegetation cover were mostly positive,while the effects of wind speed and sand content on vegetation cover were mostly negative.Among them,NDVI is significantly affected by precipitation and clay content in the northeastern part of the study area and the central and northern part of the Source of the Yangtze River,and is significantly affected by air temperature and sand content in the southeast and central and southern parts of the study area with abundant precipitation,while in the northwest part of the Source of the Yellow River,wind speed has a significant impact on vegetation coverage.更多还原